This invention relates to a process for the purification of certain wet strength resins and specifically the resins produced by the process described in U.S. application Ser. No. 21,414.
The resins involved are obtained by reacting, in an aqueous medium maintained at a temperature of 20.degree. C. or less, an epihalohydrin and a polymer comprising a backbone formed of repeating segments at least 10% of which comprise an amine group and/or partial salts thereof, substantially all of the amine groups being tertiary amine groups pendant from the polymer backbone and having a structure selected from the group consisting of ##STR1## wherein R' is either methyl or, where the nitrogen atom bears two R' groups, these together with the nitrogen can form a heterocyclic ring; R" is a divalent radical and R"' is a trivalent radical; with the unattached bond in each amine structure being attached directly to a carbon atom of the polymer backbone. The ratio of epihalohydrin molecules to tertiary amine groups in the reaction mixture is such that the transition ratio is equalled or exceeded.
The transition ratio represents a dividing line between the resins of the prior art and those obtained by the above process. The latter are characterized by their exceedingly long gel times which may be one or more orders of magnitude longer than those characterizing the resins of the prior art. The gel time is the time taken for a given resin solution or emulsion to set up, (that is to cross-link three dimensionally), once the pH is raised to a level at which the resin is activated, generally above about 8.
The resins obtained by the above process are styled "perepiquat" resins and that term shall be used in this specification. Perepiquat resins are characteristically reaction products of a poly(tertiary amine) with an epihalohydrin which have a gel time in excess of 100 minutes for a 10% solids solution at room temperature and a pH of from 10 to 13.